In the past, it was known for those requiring regular injections of a medicament, such as those having diabetes requiring injections of insulin, to use a syringe to remove a required amount of medicament from a phial, and then use the syringe to inject the required amount of medicament There are a number of drawbacks with this method. These include the fact that the loading of the syringe in this way is a delicate and somewhat skilled task, while those with, for example diabetes, are often infirm or have impaired vision, each of which increases the risk of inadvertent pricking upon the syringe. In addition, the use of syringes in public places has increasingly become socially unacceptable. To overcome these difficulties pen-type injectors have been developed.
Such injectors include within a main housing a medicament cartridge. The medicament cartridge is supplied loaded with a medicament. A user then selects a dosage and uses the pen-type injector to deliver the selected amount of medicament. The pen-type injectors are, as the name suggests, typically in the shape of a pen, though sometimes other forms are adopted. In each case, however, the appearance is non-descript so as not to draw attention to the device.
Often, the medicament Midge is replaceable to facilitate of the injector As noted above, those using such devices are often infirm or have impaired vision. There is accordingly a demand for a medicament delivery device in which an amount of a dosage of medicament to be delivered can be selected relatively quickly by the firm and infirm alike and in which the amount of the dosage may readily be controlled and determined.
It is known to provide a pen-type injector with a dose dial mechanism comprising a rotatable knob disposed at one end of the injector. The rotatable knob is connected either directly or indirectly with a drive means. The drive means acts upon a medicament cartridge located within the injector to cause medicament to be expelled from the injector. The rotatable knob conveniently comprises a helical dial. However, it is a problem with known devices of this type to display the amount of the dialed dosage of medicament on the rotatable knob in figures sufficiently large and clear to be legible by those users having a degree of impaired vision.